My brother Bill who lives in Daytona Beach Florida bought a '99 B2500 with 150K+ miles on it for $1500. I was talking to him today and he said that the 2.5 was developed by Mazda, and only Mazda, while I thought it was a joint venture with Ford. I thought that engine was called a Duratech engine and he said "No, they're not the same. The 2.5 was developed by exclusively by Mazda."

Don't have any real information to back up my statement but I thought Ford and Mazda had a partnership of sorts in that the Probe was an MX6 and Escort GT's used a Miata 1.8L engine. And the first generation Focus was developed in conjunction with the Mazda 3 (at least the suspension and chassis, if not the actual drivetrain).

Anyone care to educate me?

The 2.5L is still the Lima engine used in all 4-cylinder Rangers and B2X00's. It's just beefed up a bit and modified to get that extra fifth of a liter displacement. Fordzda did this, presumably, as a transition motor while the finishing touches were being put on Mazda's L-series motor, a.k.a. the Duratec that would eventually replace the Lima. Fordzda kept the 2.5L in place until mid-2001, when they were finally ready to introduce the new 2.3L Duratec. Although various different parts of this engine changed over time, it's ultimately what followed the Ranger & B2300 to the grave. The previous 2.5L was just all-out last-ditch effort to extend the dying Lima as far as it could go until then. When the Duratec replaced it, the Lima was forever no more.

Also, as evident from the "Fordzda" claims I made above, Ford and Mazda both spent a lot of time in each others' pants. The 2.3L Duratec NS is a longitudinal variant of Mazda's L-series motor. Ford did make a few semi-dramatic changes to it, most of which are of questionable value. For example, the head is for the 2.0L Duratec, while the block is the standard 2.3L, just modified slightly to better compliment a RWD setup. Despite this, several design aspects of the engine make it really hard to service due to clearance that just makes for more sense when installed for the FWD cars it was designed for. Ford also opted against various stability options, such as balancing shafts or variable cam timing. The logic here is iffy, but the gist seems to be that they are unnecessary in a truck application. But again, that's the future Duratec motor. Your 2.5L is still a Lima, and the upgrade of the second digit doesn't really do much to change that. Who developed what is really up for debate, but it's pretty much moot. Both sides made some weird moves, and after encountering enough of them, I really don't care who the finger is pointing at anymore.

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2003 Ford Ranger XLT
2.3L I4 Duratec DOHC, 5R44E 5-speed auto, RWD, 7.5" Open w/ 4.10 Ratio, Gibson split-rear catback
Sonic Blue Pearl with dark gray trim

Couldn't have said in better.

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MY BUILD THREAD
1999 MAZDA 2500SE, 2.5L 4-clanger, 5 speed, Green n slow. Rangers as daily drivers since 1988.
ASE Certified Mechanic, Builder of Show Destroying Protouring and Classic cars..